1. Field of the Invention
The present invention relates to a semiconductor device including a non-volatile semiconductor memory device.
2. Description of the Related Art
As a non-volatile semiconductor memory device in which a cell is placed at each intersection of a word line and a bit line arranged to be substantially orthogonal to each other, and from which stored information is read based on whether a current is flowing through the cell, there is known, e. g., a scheme which uses a tunneling magnetoresistive (TMR) element for the cell (see Jpn. Pat. Appln. KOKAI Publication No. 2004-193282). In a semiconductor memory device adopting a scheme which reads stored information by detecting a current flowing through each cell like this reference, an element which stores information by a change in resistance of each cell, and an element having a rectifying function must be connected in series as illustrated in FIG. 1 of this reference.
The reason why each cell must be constituted by series connection of the memory element and the rectification element in this manner is as follows. FIG. 1 schematically shows a semiconductor memory device. Here, three word lines (indicated as WL in the drawing) and three bit lines (indicated as BL in the drawing) are illustrated. Each square (indicated as M) in the drawing represents a memory element, and each cell is constituted of this memory element M only. For example, a consideration will be given as to a case where a judgment is made upon whether a current flows through a cell (encircled by a dotted line in the drawing) provided at an intersection of the second word line (indicated as WL2 in the drawing) and the second bit line (indicated as BL2 in the drawing). Even if this cell is in a non-conductive state, since a current flows in a path indicated by, e.g., arrows of solid lines in the drawing when surrounding cells are in a conductive state, the cell in question is determined as being in the conductive state.
Conversely, when each cell is constituted by series connection of the memory element M (indicated by a square in the drawing) and the rectification element (indicated by a diode symbol in a circuit diagram in the drawing) as shown in FIG. 2, since a current does not flow in a direction indicated by an arrow of a broken line in the drawing, the current cannot flow in a path indicated by arrows of solid lines, the current does not flow through a path connecting the word line and the bit line to which a cell in question is connected when the cell in question is in a non-conductive state irrespective of whether surrounding cells are in a conductive state, and hence whether the cell in question is in the conducive state or in the non-conductive state can be accurately read.
For this reason, in the semiconductor memory device from which stored information is read by detecting a current flowing through each cell, each cell must be constituted by series connection of an element which stores information by a change in resistance and an element having a rectifying function. Therefore, the structure becomes complicated, which obstructs miniaturization, thereby hindering improvement in memory density.
Therefore, there has been demanded realization of a semiconductor device including a non-volatile semiconductor memory device with sufficiently high memory density in which a conductive state and a non-conductive state are switched and a configuration of each cell is simplified by providing a memory element having a rectifying function in the conducive state, thus enabling miniaturization of each cell.